Thursday, November 14, 2013

A new paper finds a simple climate model based on just three variables "and taking mere seconds to run on an ordinary laptop computer, comes very close to reproducing the results of the hugely complex climate models." and "The [laptop computer] model was based on three key processes: how much energy carbon dioxide prevents from escaping to space (radiative forcing), the relationship between rate of warming and temperature, and how rapidly the ocean takes up heat (ocean thermal diffusivity)."Actually, you only need one independent variable [CO2 levels] to replicate what the highly complex supercomputer climate models output. This has been well demonstrated by Dr. Murry Salby in his lecture, which shows 1:1 agreement between the supercomputer-simulated global temperature and CO2 levels over the 21st century:

You don't even need a climate model to show what climate models predict - projections are based upon a single independent variable - CO2

That's nice, but a minor detail is that the highly complex supercomputer climate models have been falsified at confidence levels of 90% to 95% to 98%+ over the past 15-35 years, thus demonstrating that these computer games have little utility in projecting climate.

Are simple climate models nearly as good?

Modern climate models are incredibly complex, requiring many weeks and vast amounts of computing power to run. But how much difference does all the added complexity make? A new study shows that a far simpler climate model, based on just three key processes and taking mere seconds to run on an ordinary laptop computer, comes very close to reproducing the results of the hugely complex models.

The more we study climate, the more complexities appear to emerge. From clouds to ocean eddies, and from aerosols to ice melt, a bewildering array of variables acts over wildly differing timescales and distances. Modern climate models do an impressive job of capturing many of these variables, but it’s also interesting to see where the models differ.

This year, a pair of US-based climate scientists analysed how 20 of the leading atmosphere–ocean climate models in the project known as CMIP5 (Coupled Model Intercomparison Project 5) respond to an abrupt quadrupling of atmospheric carbon dioxide. Ken Caldeira from the Carnegie Institution for Science and Nathan Myhrvold, founder of patent purchasing company "Intellectual Ventures", investigated the large-scale features of each of these models, focusing in particular on the anticipated timescale of warming that they predicted.

Caldeira and Myhrvold found that the majority of the models predicted a fast onset of warming but a slow progression to a new equilibrium temperature. In most cases it took just 10 years or so to gain over half of the expected warming, but many centuries to complete the warming. After one century most models had achieved around three quarters of the expected temperature rise.

"The surprise to us was at both ends: how rapidly the first half of the warming is achieved, but also how long it took to get to the last quarter," said Caldeira, whose analysis is published inEnvironmental Research Letters (ERL). Between the models there was quite a wide range in timings, with some models achieving 60% of their expected warming in the first 10 years, while others take 100 years to achieve that level.

To provide a comparison, Caldeira and Myhrvold then ran a far simpler one-dimensional diffusion climate model. The model was based on three key processes: how much energy carbon dioxide prevents from escaping to space (radiative forcing), the relationship between rate of warming and temperature, and how rapidly the ocean takes up heat (ocean thermal diffusivity). Despite its lack of complexity the simpler model did an amazingly good job, reproducing all but 0.16°C of the warming predicted by the complex climate models under the same circumstances. This suggests that the three processes upon which the simple model is based control most of the variation in Earth’s climate.

"Remarkably we found that all of these incredibly complex models that can take weeks of computer time with thousands of processors can in fact be summarized with good accuracy to just three key processes," explained Myhrvold.

The findings indicate that the complex details of climate may not really make so much difference after all. "It means that we could approximate the results of a full-blown climate model with a vastly simpler model, taking just fractions of seconds to run on a laptop," said Myhrvold.